Summary: The goal of this project is to develop molecular methods for consistency monitoring of live viral vaccines. During this year of the project we have focused on Mumps Vaccine Live (MVL) we have determined complete nucleotide sequences of several strains and sub-strains of the vaccine, and created quantitative assays for measring the amount of mutant virus in vaccine samples. Molecular markers of consistency of Urabe AM9 strains were identified, and MAPREC assays created to determine mutational profiles of commercial products. Two sub-strains of Jeryl Lynn strain present in commercial product made by Merck were completely sequences. MAPREC test for determination of ratio of the sub-strains in vaccine lots were created. We have also developed a new rapid quantitative assay which can be used for the same purpose. The new method is based on MALDI-TOF mass-spectrometry. It was shown to produce results that are identical to those generated by MAPREC.